Method for dressing grinding wheels



Feb. 26, 1963 P. R. THOMAS 3,078,835

METHOD FOR DRESSING GRINDING WHEELS Filed May 27, 1960 INVENTOR. Philip R Thomas HIS A TTORNE Y 3,078,335 METHGl) FOR DRESSING GRINDING WHEELS Philip R. Thomas, Livonia, Mich, assignor to The Carborundurn Company, Niagara Falls, N.Y., a corporation of Delaware Filed May 27, 1960, Ser. No. 32,150 4 Claims. (Cl. 12511) This invention relates to the art of cylindrical grinding, and more particularly to a method of dressing centerless grinders and to a dressing pin used therein. Further, this invention relates to a method of dressing wheels for center-type grinders and to a wheel dresser for use therein.

Centerless grinding wheels are well known in the art. They are particularly useful for precision work in which large numbers of relatively small pieces are to be ground and the ground surfaces bear no exact relationship to another surface except as a whole. No chucking of the work on mandrels or other holding devices is required, yet the work is rigidly supported and there is no tendency for chatter or deflection of the work. Since a true floating condition exists during the grinding process, less grinding stock is required. Less skill is required in the operation of centerless grinders than in the operation of other cylindrical grinders. However, in order to obtain precise work having a minimum taper and a high finish, the center-less grinder must be meticulously adjusted. Such adjustments are not only diflicult to make, but require substantial time while the machine is idle. My invention provides a method whereby precise adjustment can be made with little effort and in a minimum amount of time. I have found that by passing a diamond impregnated pin through a centerless grinder, the grinder can be automatically adjusted and the final precise manual adjustment now required can be eliminated.

This invention also provides a method for improved dressing of grinding wheels used in center-type grinders and to a wheel dresser for use therein.

In the drawings, FIGURE 1 is a diagrammatic view of a centerless grinder;

FiGURE 2 is a side elevation of the grinder shown in FEGURE 1;

FEGURE 3 is a longitudinal section taken through a diamond dressing pin made according to this invention; and

FIGURE 4 is a plan view of a pin-type wheel dresser, made in accordance with the present invention, for use in dressing a center-type grinding machine wheel.

As shown in the drawings, a centerless grinder comprises a grinding wheel 10- and a regulating wheel 12.

7 Any conventional grinding wheel such as a vitrified bonded alumina wheel may be used. The regulating wheel is generally smaller than the grinding wheel and is composed of a rubber-bonded abrasive such as alumina. A work piece 14 is supported between the wheels 10 and 12 on a work rest 16. The regulating wheel 7.2 has frictional characteristics which enable it to rotate the work at its own rotational speed. Axial movement or" the work past the grinding wheel is obtained by tilting the regulating wheel at a slight angle from the horizontal as shown at 18 in FIGURE 2. This angle may vary from to 8 or degrees. The larger the angle, the faster the rate of feed.

Two types of dressing are generally used for grinding wheels. In an open dress technique, a diamond tipped dressing tool is passed over the surface of the grinding wheel as many times as necessary to true up the wheel at an infeed of about .001 per pass and at a lateral speed of about 20 per minute. In fine dress technique, the lateral speed is reduced to 4" per minute and the initial infeed passes at .001" per pass are followed by two addi- 3,078,835 Patented Feb. 26, 1963 tional passes using an infeed of .0005 per pass and two passes using an infeed of .0002 per pass. The open dress is quicker, but the fine dress produces a better finish. Irrespective of which technique is used, it is common to encounter a taper condition which must be manually corrected by adjustment of the axes of rotation of the grinding wheel and the regulating wheel so that the faces of the two wheels are aligned, i.e., so disposed that the portions of the wheels which contact the work piece are parallel within the permissible tolerance. This troublesome and time-consuming operation can be eliminated by the use of my invention.

My new method comprises passing a diamond coated dressing pin through the centerless grinder after the conventional open or fine dress has been completed. The feed or speed at which the pin is run through the grinder is not critical. However, I prefer to use the same feed as will be used in the grinding operation. This step corrects for small inaccuracies of machine set since it not only dresses the grinding wheel but also dresses the feed wheel to produce a dead-true alignment. Where the dressing pin is the same diameter as the finish dimension of the workpiece, the final precise adjustment of the machine by hand is eliminated since this is done by the pin which trues both the grinding and feed wheels into dead true alignment. Furthermore, the use of a diamond dressing pin eliminates irregularities in the wheel surface and any build-up on the work rest blade.

As shown in FIGURE 3, a diamond dressing pin 19, used in my new method, comprises a steel core 20 to which an abrasive section 22 consisting of bonded diamond grains is brazed. Any conventional type of bond may be used. I have successfully used a tungsten carbide and cobalt bond. In that instance, a mix consisting of .375 gram of diamond grit, 2.99 grams of tungsten carbide and 2.45 grams of cobalt was hot pressed in a graphite mold at a temperature of approximately 1300" C. and a pressure of 3000-4000 psi. to form an abrasive section /2 long having an inside diameter of and an outside diameter of Three such sections were brazed to a steel core in diameter and 1 /2" long.

The following specific examples will serve to illustrate the effectiveness of my invention as applied to centerless grinding.

Example I A Cincinnati Centerless Grinder having a vitrified bonded 60 grit alumina grinding wheel with a 20" diameter and 6" face and a rubber bonded grit alumina regulating wheel with'an 11" diameter and a 6" face was used to compare an open type dress without a pin dress and an open type dress followed by a pin dress according to my invention. Also, in one instance, the open type dress was followed by the customary precise manual adjustment. The dressing tool was of the cluster type, a cluster of diamonds being embedded in the end of a tungsten carbide rod. The work rest blade was made of tungsten carbide and had a 30 angle. A 2 draw angle was used. The diamond dressing pin was 1 /2" long and in diameter consisting of a thick abrasive section brazed to a mild steel pin. The results of the tests are tabulated below.

3 Example [I A test was also made identical in all respects to that discussed in Example I except that a fine dress was sub- The foregoing results show clearly that by using my new process and dressing pin, the final precise adjustment of the centerless grinder may be eliminated without any sacrifice in accuracy of the set. Small inaccuracies in machine set are corrected by running my pin through the centerless grinder as described.

While the embodiment of the present invention illustrated in FIGURE 3 has been shown as having a uniform diameter, it is to be considered within the scope of the invention to fabricate the dressing pin in a stepped configuration for use in dressing wheels for the production of infeed finished articles. In this method of operation, the grinding wheel is dressed to stepped configuration and the work piece is fed into the wheel and then withdrawn, as contrasted to a through feed type of operation where articles of uniform diameter are produced by feeding the work piece into one side of the machine and out the other side. v

The concept of the present invention is also applicable to cylindrical grinders of the center-type. In these machines the work piece, or the piece to be ground, is supported between a pair of aligned centers and rotated. While so supported, a rotating grinding wheel is engaged with the surface of the work piece to effect a grinding operation thereon.

As shown in FIGURE 4, a dressing pin made in accordance with the present invention is so fabricated as to be supported by the centers of the grinding machine as a work piece would be supported. In this embodiment the diamond dressing pin 24 is of the same general structure as the pin 19 illustrated in FIGURE 3. Thus it comprises a core 26 and an abrasive section or shell 28 therearound. However, the core is of elongated configuration and extends beyond each end of the abrasive section 28. The core is suitably shaped at each end to provide center holes 30, whereby the pin 24 can be supported between the centers (not shown) of a center-type cylindrical grinding machine. The periphery of the abrasive section 28 can be of greater or lesser width than the grinding wheel to be dressed thereby. In FIGURE 4 the width of the grinding wheel 32 is illustrated as being narrower than the abrasive section.

The abrasive section 28 of the pin 24 is shown as being substantially at the longitudinal center of the core 26. However, it is to be considered within the scope of the invention to place the abrasive section at any position on the core. Also it is within the scope of the invention to form the abrasive section as a stepped configuration for dressing a grinding wheel of stepped configuration.

. The diameter of the pin of the present invention, as applied to centerless grinding, will vary with the diameter of the work piece.

Though they need not be exactly the same size as the finish dimension of the Work piece, this is an optimum operation goal, as hereinbefore described. When applied to center-type grinding, the diameter of the dressing pin can be substantially greater or less than the dimeter of the work piece.

While, as described above, a steel core can be utilized in all instances, it is preferred for convenience of manufacture, to form the pin entirely of bonded diamond grain when the diameter is less than /2". When the diameter is /2" or greater, the structure will preferably contain a steel core, because of economic considerations. In the larger sizes, the bonded diamond grain will have a thickness in the range from about g" to about Mr. Preferably the bonded diamond grain will have a thickness in the range from about to about '-}f;

Bonds applicable to use in forming the abrasive section of pins of the present invention include bronze, tungsten carbide, steel and the like. The essential factor is that the bond be very strong to retain the grains of diamond in place during the dressing operation and thus assure long life to the dressing pin.

The diamond content of dressing pins made in accordance with the present invention can vary over a substantial range. In the trade a diamond concentration of denotes 72 carats by weight of diamond per cubic inch of abrasive matrix. Thus the diamond concentration of the pins of the present invention can vary over the range from 12 /2 to 150. This means that from about 17 carats per cubic inch to about 108 carats per cubic inch of bonded matrix can be employed.

While I have described my invention in terms of the presently preferred embodiments, it should be understood that it may be otherwise embodied within the scope of the following claims.

I claim:

l. In a method of dressing centerless grinders having a grmding wheel, a regulating wheel, and a work rest, the step of passing a cylindrical diamond dressing pin between and in contact with the wheels in a path substantially parallel with the axis of rotation of said grindmg wheel while said wheels are rotating and while said dressing pin is supported on said work rest.

2. A method as set forth in claim 1 in which said dressmg pin is of substantially the same diameter as the work piece to be ground.

3. A method of dressing centerless grinders having a grinding wheel, a regulating wheel, and a work rest which comprises the steps of initially dressing the peripheral surface of said grinding wheel, relatively adjusting the axes of said grinding wheel and said regulating wheel so that said axes lie in vertical planes that are substantially parallel, and thereafter finally dressing the peripheral surfaces of both of said wheels while said wheels are ro tating by passing a cylindrical diamond dressing pin, supported on said work rest, between and in contact with said wheels in a path substantially parallel with the axis of said grinding wheel, whereby to eliminate irregularities in the wheel surfaces and correct for small inaccuracies of machine setting so that the wheels are in true alignment.

4. In a method of dressing centerless grinders having a grinding wheel, a regulating wheel, and a work rest, the steps of placing a cylindrical diamond dressing pin between and in contact with said wheels while said wheels are rotating and drawing said dressing pin through said grinder by said regulating wheel in a path substantially parallel with the axis of rotation of said grinding wheel while said dressing pin is supported on said work rest.

References Cited in the file of this patent UNITED STATES PATENTS 1,099,984 Kirsten June 16, 1914 2,413,167 Bugley Dec. 24, 1946 2,704,705 Gifford Mar. 22, 1955 2,730,848 Wallace Jan. 17, 1956 2,896,377 Walkling July 28, 1959 FOREIGN PATENTS 604,950 Great Britain July 13, 1948 

1. IN A METHOD OF DRESSING CENTERLESS GRINDERS HAVING A GRINDING WHEEL, A REGULATING WHEEL, AND A WORK REST, THE STEP OF PASSING A CYLINDRICAL DIAMOND DRESSING PIN BETWEEN AND IN CONTACT WITH THE WHEELS IN A PATH SUBSTANTIALLY PARALLEL WITH THE AXIS OF ROTATION OF SAID GRINDING WHEEL WHILE SAID WHEELS ARE ROTATING AND WHILE SAID DRESSING PIN IS SUPPORTED ON SAID WORK REST. 